The process of laser cutting uses a laser to cut materials for industrial manufacturing applications, and more recently in academia, small businesses and in the home environment for hobbyists. Laser cutting machines direct a laser at the material to be cut. The material then melts, burns, vaporizes away, or is blown away by a jet of gas, leaving an edge with a high-quality surface finish. Industrial laser cutters are used to cut flat-sheet material, as well as structural and piping materials.
A computer controlled laser cutting machine includes multiple components. In general, these components at least consist of the cutting laser, optics for conditioning and focusing the laser beam, at least one actuator to position the cutting laser, and a computer based controller which commands the actuators to move the cutting laser in such a way as to produce the desired cut pattern.
In practice there is variation in the performance of each component and variation in the way the components are assembled to form the overall machine. These variations can be either static or dynamic for a particular component or complete machine. Static variations remain constant with time. The magnitude of dynamic variations changes over time. All of these variations can produce errors in the position of the cutting laser beam relative to its desired position, and thus produce errors in the final product. It is therefore desirable to have a system and a method for calibrating the laser cutting machine, such that the above errors can be corrected and the accuracy of the machine improved.
In addition to the need for calibration, there is also a need to determine a cutting path of a laser beam, i.e., the path traversed along the work surface by the cutting laser beam during the cutting process. Some types of path errors are only present during full speed operation, such as errors caused by vibrations of the laser cutting machine and errors caused by position control processes. The ability to record the cutting path in real time provides an insight into the dynamics of the system.
The simplest method for measuring an error in the cut path is to measure the cutting path manually. This process is labor intensive, time consuming, and requires expensive measurement equipment. Calibration may need to be performed several times a day due to variations temperature, and manual error measurements can not be made during full speed cutting operations.
One calibration method uses a camera based system for correcting optical path errors. Prior to processing, the laser beam is used to illuminate the area of the workpiece to be processed. The camera records an image, and a controller uses the image to correct the optical path prior to machining. High accuracy can be achieved in this manner, but a large amount of time is wasted by performing a calibration before each cut. In addition, this type of calibration system is not suitable for continuous laser cutting.
Another method uses a camera to calibrate the controller of a laser processing system. The controller commands the deflection system to scan the optical path over a calibration plate while the camera records images of the pattern on the surface of the calibration plate. The images are then processed to determine the error in the optical path, which is in turn used as feedback for the controller to compensate the path. This calibration is performed periodically, at the start of each shift for instance, and is therefore suitable for use in laser processing systems that cut continuously. However, the camera can be expensive, and the image processing is time consuming. The amount of time required to process each image may prevent such a system from being used to record the cut path in real time.
Accordingly, there is a need in the art for a method suitable for calibrating a laser cutting machine. There is also a need to provide such a method that can calibrate the operation of the laser cutting machine during full speed operation.